Comparison of risk of malignancy and predictive value of diagnostic categories defined by Papanicolaou Society of Cytopathology system and WHO reporting system for pancreaticobiliary cytopathology in solid pancreatic lesions

Abstract

Background: The standardized diagnostic categories defined by the World Health Organization (WHO) reporting system support the interdisciplinary interpretation of cytological findings in the management of pancreatic cancer. Objective: To compare this classification to the Papanicolaou Society of Cytopathology (PSC) system in terms of predictive value and risk of malignancy (ROM) in solid pancreatic lesions. Design: Retrospective cohort study. Methods: All consecutive patients with solid pancreatic lesions who underwent endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) sampling at the University of Szeged from 2014 to 2021 were retrospectively enrolled. The predictive value and ROM of cytological findings were determined with comparison to histologic outcome and/or clinical follow-up. Results: A total of 521 EUS-FNAs were performed with a malignancy rate of 81.76%. In both classification systems, the absolute ROM of “non-diagnostic,” “negative for malignancy,” “atypical,” “suspicious for malignancy,” and “malignant” categories were 48.2%, 2.3%, 78.1%, 100.0%, and 99.4%, respectively. Despite the heterogeneous nature of the “neoplastic: other” category of the PSC system, the absolute ROM for solid lesions was 100%. Pancreatic neoplasm: high-risk/grade category including only two endosonographically solid cases of high-grade intraductal papillary mucinous neoplasms showed 100% ROM. There were no differences between PSC and WHO systems in sensitivity, specificity, and negative and positive predictive values: excluding the “atypical” category, these were 99.7%, 95.6%, 97.7%, and 99.5%, respectively. The “atypical” category considered benign resulted in a higher decrease in validity and negative predictive value, compared to “atypical” considered true malignant (93.6% vs 97.7% and 65.8% vs 97.7%). Conclusion: For solid pancreatic lesions, the WHO system was identical to the PSC system in terms of ROM and predictive values.